Both the diagnostic and quantitative accuracy of radionuclide imaging are limited by finite spatial resolution, high scatter, and image noise. Conventional (non-medical) image processing techniques to improve resolution typically do so at the expense of noise; those to reduce noise do so at the expense of resolution. We and others have used two- dimensional Fourier filtering for image restoration (improved contrast) and noise suppression. While studies have demonstrated the potential of such filtering to improve image quality and quantitative accuracy no study has determined the degree of enhancement possible, not explicitly optimized filter parameters for subjective interpretation or quantification of specific SPECT and PET studies. We propose to: assess the limits of spatial resolution recovery, scatter reduction, and noise suppression achievable with two-dimensional Fourier filtering in brain and heart studies; assess the effects of two different "optimization" approaches (i.e., analytical derivation and subjective definition) on accuracy of visual interpretation of SPECT studies in the diagnosis of coronary artery disease, including assessment of overall accuracy, that in selected patient subgroups, and the degree of variation in the actual filters producted; and determine the effects of Fourier filtering on the accuracy of quantification of regional myocardial perfusion. The Wiener filter, with several different implementations, will be used as a model two-dimensional Fourier filter. Phantoms will be used to assess the degree of image restoration achievable over a range of filter parameters and phantom characteristics. Human data from patients undergoing coronary angiography will be used to assess benefits in the diagnosis of coronary artery disease. These data will be analyzed by receiver operating characteristic analysis. Data from dogs, in whom single-vessel ligations are created, will be used to assess the accuracy of quantification of perfusion. These data will be correlated with microsphere measurements of regional blood flow.